It is commonly known in the art of container fabrication to fabricate containers by the stretch blow molding process. In the stretch blow molding process, a substantially tubular parison or “preform” is provided, being fabricated from a thermoplastic and having an open end near a mouth and a closed end opposite the open end. The preform is disposed within a mold having a cavity substantially defining the form and contours of a container.
The preform is expanded into the cavity of the mold by the action of a working fluid injected into the preform under pressure, and by the action of a stretching rod inserted into a mouth of the preform. The pressurized fluid causes the preform to inflate, expanding primarily radially. The stretching rod is advanced into the preform and presses against an opposite interior surface, stretching it longitudinally into the mold.
Conventionally, the pressurized fluid injected during the molding of the container is air, usually heated to facilitate the deformation of the preform. However, it is known to use a liquid as the working fluid, preferably the liquid which is ultimately to be packaged within the container. In this way, the process of forming a container and filling it with a product are effectively combined, realizing great advantages in equipment cost and production efficiency compared to an air-injection stretch blow molding system.
When filling a container with a liquid, it is necessary to leave a small void space at the top of the container. This void space enables the consumer to open the container without spilling any of the liquid contained therein, as well as provides compensation for any thermal expansion of the liquid during storage.
In processes where the fabrication and filling of the container are carried out in separate steps, providing this void space is a relatively trivial matter. In a process so configured, one need only dispense a volume of liquid product into the container during the filling step that is less than the total volume of the container by the desired amount, leaving the necessary void space in the container.
In a combined forming-filling container fabrication process, however, this is not a feasible option. Specifically, in order to ensure that the preform is fully expanded into the cavity of the mold and that all of the contours of the resulting container are fully formed, one must inject a volume of liquid equal to the full, final volume of the container. The resulting container is thus filled to the brim with the liquid product.
When using a combined forming-filling process combined with a stretching step of the preform, the stretching rod does occupy some volume within the container, and retracting it at the completion of the forming-filling process will create a small amount of void space in the container. The void space created by the displacement of the stretching rod, however, is not always sufficient for the prevention of spilling when the container is opened, especially where a particularly thin stretching rod is employed.
Increasing the diameter of the stretching rod will increase the volume of the void space ultimately created in the container; however, the space between the stretching rod and the interior surface of the mouth of the container are coordinately reduced, impeding the injection of the liquid during the forming of the container. It is therefore necessary to remove some of the liquid from the container upon the completion of the injection process.
One solution to this is to remove a small amount of the liquid by suction, in particular by sucking some of the liquid back through the means for injecting it into the preform during the fabrication of the container. In particular, the document WO 2010/003853 A1 describes a stretch blow molding system in which the stretching rod is hollow, and contains at least one port at a distal end through which this extra liquid may be aspirated from the beverage container.
While this system produces acceptable filled containers, it is disadvantageous in several aspects. First, the at least one port in the stretching rod must remain sealed during the injection of the liquid, which increases the complexity of the apparatus and the expense of its manufacture and operation. Furthermore, the channel within the stretching rod is difficult and time-consuming to clean as the apparatus must be at least partially disassembled to give access to the entire channel. In addition, dissolved material in the liquid will tend to form accretions in the narrow channel and ports, a particularly acute problem when the liquid is mineral water. These accretions reduce the flow through the hollow stretching rod, requiring time-consuming cleaning and maintenance to maintain efficient functioning of the apparatus.
It is therefore an object of this invention to provide a method for fabricating and filling a beverage container which accurately provides a void space in a formed and filled container without the disadvantageous aspects of the apparatuses known in the art.